Typically, a thermal transfer recording medium is called a thermal ribbon and refers to an ink ribbon used in a thermal transfer printer. In such a thermal transfer recording medium, a thermal transfer layer is formed on one surface of a substrate, and a heat-resistant sliding layer (so-called, “backcoat layer”) is formed on the other surface of the substrate. The thermal transfer layer described herein is a layer containing ink, in which this ink is sublimated (sublimation thermal transfer type) or fused (fusion thermal transfer type) by heat generated in a thermal head of a printer to be transferred to a transfer medium side.
Currently, by using the sublimation thermal transfer type among the thermal transfer types in combination with high-performance printers, various full-color images can be simply formed. Therefore, the sublimation thermal transfer type is widely used for self-printing of digital camera photos and for printing cards such as ID cards, printed materials for fun, and the like. Along with such diversification of uses, demands for decrease in size, increase in speed, decrease in cost, and durability of printed materials to be obtained have increased. In addition, recently, a thermal transfer recording medium including, on the same side of a substrate sheet, a protective layer or the like that imparts durability to printed materials and plural thermal transfer layers that are provided so as not to overlap the protective layer or the like has been widely used.
In such circumstances, along with the diversification and the expansion of uses, the printing speed of printers has been further increased. As a result, in a thermal transfer recording medium of the related art, a problem that a sufficient print density is not obtained has occurred. Therefore, in order to increase transfer sensitivity, an attempt to improve transfer sensitivity during printing has been made by decreasing the thickness of a thermal transfer recording medium. However, when the transfer sensitivity is increased, during the manufacturing of a thermal transfer recording medium or printing, wrinkling may occur due to heat, pressure, or the like. In addition, in some cases, a thermal transfer recording medium may be broken.
In addition, an attempt to improve print density and transfer sensitivity during printing has been made by increasing a ratio of dye/resin (Dye/Binder) on a dye layer of a thermal transfer recording medium. However, when the amount of a dye is increased, not only the cost increases, but also a part of the dye may be transferred (set off) to a heat-resistant sliding layer of a thermal transfer recording medium during winding in a manufacturing process. In addition, during rewinding as a subsequent process, the transferred dye may be transferred again (set off again) to another color dye layer or a protective layer. When this contaminated layer is thermally transferred to a transfer medium, a different color from a designated color may be printed, or so-called scumming may occur.
In addition, an attempt to increase energy during image forming not only on a thermal transfer recording medium side but also on a printer side has been made. However, when the energy during image forming is increased, power consumption is increased, and the service life of a thermal head of a printer may be decreased. In addition, fusion bonding between a dye layer and a transfer medium, so-called, abnormal transfer is likely to occur. To deal with this problem, when a large amount of release agent is added to a dye layer or a transfer medium to prevent abnormal transfer, bleeding or scumming may occur on an image.
In order to satisfy the above-described demands, several methods are proposed. For example, PTL 1 proposes a thermal transfer sheet including an adhesive layer between a substrate and a dye layer, the adhesive layer containing a polyvinyl pyrrolidone resin and a modified polyvinyl pyrrolidone resin.
In addition, PTL 2 proposes a thermal transfer sheet including an adhesive layer between a substrate and a dye layer, the adhesive layer containing a thermoplastic resin such as a polyvinyl pyrrolidone resin or a polyvinyl alcohol resin and colloidal inorganic pigment ultrafine particles.